In this study, the delignification kinetics of tetrahydrofurfuryl alcohol (THFA)/HCl pulping of rice straw was investigated. In the atmospheric pressure pulping, two phases of different delignification rates were observed which were closely related to the amount of HCl and temperature. Equations for the transition time of these two phases at various temperatures and catalyst dosages were derived. For optimal cooking control, the transition time of these two phases can be calculated. The cooking showed very low activation energies, which, in phase I and phase II, were only 26.5 kJ and. 32.2 kJ mol(-1), respectively. At phase I pulping, delignification was the main reaction with minimal dissolution of carbohydrate fractions. Consequently, the yield loss was low. In phase H, however, when the residual lignin content was less than about 5%, the dissolution of the carbohydrate was greater than the lignin removal, causing a marked reduction in pulp yield. Comparisons of K-L/K-C (ratio of delignification rate and rate of carbohydrate dissolution) and Delta(L)/Delta(C) (ratio of lignin removed and carbohydrate dissolved during pulping) values in phases I and II were made. Results showed that both values were greater in phase I, and both values reached their maxima at 120 degrees C and catalyst dosage of 0.020 mol L-1.